The Starting Argument in the Zombie Attack

Your brain starts to deteriorate and the doctors replace it,
piecemeal, with silicon chip workalikes, until there is only
silicon inside your refurbished cranium.

ASearle, at
least three distinct possibilities arise:

V1

The Smooth-as-Silk Variation:

V2

The Zombie Variation:

V3

The Curare Variation:

Searle wants to draw a certain conclusion from V2:

In [V2] we imagined that the mediating relationship between the
mind and the behavior patterns was broken. In this case, the silicon
chips did not duplicate the causal powers of the brain to produce
conscious mental states, they only duplicated certain input-output
functions of the brain. The underlying conscious mental life was left
out ([3], 68).

And here is Dennett's reaction:

But that is only one of the logically possible interpretations of his
second variation The other is the crucial one: while you are
dying, another consciousness is taking over your body. The speech
acts you faintly hear your body uttering are not yours, but they are
also not nobody's! I cannot see how Searle could simply have
overlooked this gaping loophole in his thought-experiment. But
there it is I am baffled ([2], 198-9).

But what exactly does
Searle want from V2? He tells us explicitly on
page 69 of
The Rediscovery of
the Mind
that he wants to establish via V2 and V3 that a certain trio
of propositions is inconsistent. The trio, reproduced verbatim (p. 69):

(1)

Brains cause conscious mental phenomena.

(2)

There is some sort
of conceptual or logical connection between conscious mental
phenomena and external behavior.

(3)

The capacity of the brain to
cause consciousness is conceptually distinct from its capacity to cause
motor behavior. A system could have consciousness without
behavior and behavior without consciousness.

Represent the three
propositions using elementary logical machinery: Bx iff x is a brain;
Mx iff x causes (a full range of) mental phenomena; and Ex iff x
causes (a full range of) external behavior. Then the trio, with
Searle's underlying modal notions brought to the surface, and a
denoting the brain of the character in our thought-experiments,
becomes

(1 )

(2 )

(3 )

The set {(1 ), (2 ), (3 )} is provably
inconsistent, in garden variety
contexts; the proof is trivial, for
example, in quantificational S5 (which I
happen to like) and the weaker T.

Proof. Proposition
(1 ) is superfluous. Then, e.g., instantiate appropriately on axiom-
schema T to get, with (2 ), by modus ponens,
;
instantiate to , derive by
propositional logic that
, rewrite this by
the rule known as necessitation to ,
and in
turn rewrite this as , and then, by double
negation, as , which of course
contradicts (3 )'s
first conjunct.

And just as clearly this logical
possibility implies the second conjunction of (3 ) (and
V3 implies
the first conjunction).

Now, Searle's ultimate aim is probably not to
show {(1), (2), (3)} or its formal correlate inconsistent,
for reaching this aim, as we have seen, is a matter of some pretty
straightforward
logic.

Rather, Searle aims
no doubt to refute the claim that there is a
conceptual connection between conscious mentality and behavior,
that is, he seeks to demonstrate the truth of (3 ) and the falsity of
(2 ).

This is a result which follows when the inconsistency we have noted is
combined with V2 , V3 and
(( V2 V3 ) (3 )).